Lithographic methods are at the heart of modem day microfabrication, nanotechnology and molecular electronics. A variety of scanning probe lithography (SPL) techniques have been developed.
One such technique is dip pen nanolithograpy (DPN). See, e.g., Piner et al., Science, 283, 661-663 (1999); Hong et al., Science, 286, 523-528 (1999); Weinberger et al., Advanced Materials, 12, 1600-1603 (2000); Mirkin et al., CHEMPHYSCHEM., 2, 37-39 (2001); and PCT application WO 00/41213. DPN is a nanolithography technique by which molecules are directly transported to a substrate of interest in a positive printing mode. DPN utilizes a solid substrate as the “paper” and a scanning probe microscope (SPM) tip (e.g., an atomic force microscope (AFM) tip) as the “pen”. The tip is coated with a patterning compound (the “ink”), and the coated tip is used to apply the patterning compound to the substrate to produce a desired pattern.
There are also a variety of negative printing techniques that rely on scanning probe instruments to pattern substrates using self-assembling monolayers and other organic materials as resist layers. See, e.g., Bottomley, Anal. Chem., 70:425R (1998); Nyffenegger et al., Chem. Rev., 97:1195 (1997); Schoer et al., Langmuir, 13:2323 (1997); Xu et al., Langmuir, 13:127 (1997); Perkins et al., Appl. Phys. Lett., 68:550 (1996); Xu and Liu, Langmuir, 13, 127-129 (1997); Langmuir et al., J. Vac. Sci. Technol. A, 14:1223 (1996); Muller et al., J. Vac. Sci. Technol. B, 13:2846 (1995); Abbott et al., Science, 257, 1380-1382 (1992); and U.S. Pat. No. 5,922,214. One such technique is nanografting. See Xu and Liu, Langmuir, 13, 127-129 (1997) and U.S. Pat. No. 5,922,214. In nanografting, a layer of material on a substrate is mechanically displaced using an AFM tip. The displacement is carried out in a fluid containing molecules which rapidly enter the void created by the AFM tip and bind to the clean substrate surface. A third technique is the nanopen reader and writer (NPRW) technique which combines DPN and nanografting. See Amro et al., Langmuir, 16, 3006-3009 (2000). A monolayer of molecules on a substrate is used as a resist, and an AFM tip is used to displace molecules of the monolayer from desired locations. The tip is pre-coated with molecules different from the molecules that form the monolayer. As the tip displaces the molecules of the monolayer, the molecules on the tip adsorb onto the freshly exposed substrate following the track of the tip.
Microfabrication techniques such as photolithography, microcontact printing, micromachining, and microwriting can produce patterns as small as 100 nm, but the production of sub-100 nm structures still poses a challenge. Amro et al., Langmuir, 16, 3006-3009 (2000). At present, such high-resolution fabrication can be achieved using SPL techniques. Id. Accordingly, additional and improved SPL techniques would be highly desirable for use in a variety of fields.